Vacuum tube



Jam. w, 1928.

H. E. METcALF VACUUM TUBE Filed Jan.2l, 1925 :Patented Jaa. 1o, '1928.

UNITED STATES PATENT OFFICE.

HERBERT E. IIETCALF, OF SAN LEANDRO, CALIFORNIA, ASSIGNOR TO THEMAGNAYOX C0., F SAN FRANCISCO,v CALIFORNIA, A CORPORATION OF ARIZONA.

VACUUM TUBE.

Application mea January a1, 1925. serial No. 3,772.

4This invention relates to vacuum tubes of the three-electrode type; 'Inprinciple the present tube resembles that ofa prior application tiled byme July 23, 1924, Serial Number 727,708, in that use is made of acontrol electrode which does not obstruct the iiow of electrons betweenthe filament' and .the plate. In said prior applicati n I employed acontrol electrode in the f rm of a. thin plate having slots lwithstraight edges disposed at opposite sides of the filament. In practicethe current output was notv as great as is desirable for many purposes,owing to the fact' thatv the electron discharge from the controlelectrode to the filament was concentrated .in a lthin field and actedto choke oil the flow of electrons from the tilament to the anode. l

I nd that by fr-ming one or both edges of this control electrode withteeth or 1ndentations this condition is eliminated and' the sameamplification is maintained, but the current output is enormouslyincreased. In other words, .the teeth will concentrate on the filamentand the spaces between the teeth will allow for free passage ofelectrons from the filament to the anode. Also a somewhat wider eld ofelectron discharge is obtained by the use of these teeth, and this 30field can be considerably'A widened by spreadilthe teeth laterally a artand therefore the culty of aligning t e fllament and elec. trode isconsiderably minimized.-

In the accompanying drawings, .A -Fi 1 is a perspective view of apreferred form of my invention;

Fig..2'is a side elevation of the same; Fig. 3 'is a cross-section ofthe preferred form of tube;

Fig. 4 is a` diagrammatic view of a modified arrangement; and

Fig. 5 shows a still further modification of the control electrode.

Fi 6 shows a sectional view taken on 45. the llne 6-'-6 of Fig. 2.

Referringin detail to the accompanying drawin I show a sealed vesselortube 10 containing anodes 11 of.any.`desired form,

but preferaby in the form ofspecial plates.

Between these plates is a control electrode` 50 12 in the form of a thinplate arranged midway between the anode plates and parallel therewith.This control electrode has a V- shaped slot in which is arranged afilament 13. The filament is looped over aspring :515l

metal arm 14 which will yieldto accommodate elongation of the filamentwhen the latter is heated. The filament occupies the position shown inFig. 2 when cold, but when heated it will be substantially equidistantfrom the edges of the slots.

These slots are formed with teeth or indent-ations 15 for the purposeabove mentioned, and preferably, but not necessarily, these teetharespread apart in a lateral 55 direction so as to form a broader field vofelectron discharge and minimize the difficulty of aligning the filamentwith the edges.' of the slots. In other words the filament is loopedover a relatively wide springand the strands are not in the same plane.By spreading the teeth laterally or by'spreading the legs of the plateapart as shown in. Fig.

4, the eld of action of the control electrodecan be concentrated tobetter advantage on the filament.

In the modification of Fig. 5 I' show two rows of teeth 16 at eitherside of the filament. The action is the same'as in the preceding forms,except that a wider field is afforded.

To a certain extent these teeth function somewhat after the manner ofthe strands of the o dinary grid, but unlike the grid, no obstruction isplaced in the path of the electron discharge between the filament andanode. I

This tube has a lower internal capacity Athan prior tubes, and isadmirably adapted to radio frequency and detector purposes. Theconstruction and assembly of such a tube is considerably less expensivethan where the ordinaryform of grid is employed.l The present'controlelectrode can be stamped out in a single operation and from a 'singlepiece of metal, and the work of assembly is l simplified by reason ofthe fact that the filament need not be fished through the strands What Iclaim as new and desire to secure of the grid as in prior devices. byLetters Patent is: 10

It w111 be understood that many changes A control electrode for vacuumtubes comin the construction and arrangement of the prising a plate-likemember formed with a several parts herein shown and describedsubstantially V-shaped slot to receive the {ilamay be made Withoutdeparting from the ment, the Iedges of the slot being provided spirit ofm invention as disclosed in the with indentations. appended c aim.HERBERT E. METCALF.

